And the possibility of living organisms on Mars could still not be ruled out. Now, you should realize that it is a lot easier to prove that something exists than it is to prove that something doesn’t exist. Once you’ve discovered something, you’ve got it in the bag――but it’s harder to prove that something is not there, because no matter how much you look without finding it, it could still be hiding under the next rock. So scientists continue to look under the Martian rocks. The Viking mission in 1976 included three biological experiments――the Labelled Release experiment, the Pyrolytic Release experiment, and the Gas Exchange experiment. None of these experiments were successful. That is, none of them produced clear results detecting life forms. Most scientists now agree that the experiments were flawed――all of the results can be explained as purely chemical processes that do not require the presence of life. However, there is now evidence, as I said, that Mars once had significantly more water, and now scientists are considering the possibility that the planet once had life――but that it went extinct when conditions on Mars got worse.
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